A new generation of curved displays for Smartphones and TVs has just
been launched. While there have been curved screens around before, they were
actually just flat displays with a curved cover glass on top. This time the
displays themselves are actually curved and that makes a significant
difference.

There is widespread misunderstanding regarding curved displays. They
aren't simply a marketing gimmick as has been widely reported – we’ll show that
curved screens substantially improve the display performance. In fact,
curved screens are a major and very important new display technology
innovation, particularly for handheld Smartphones.

Curved displays are possible now because of the availability of thin
curved glass and developments in display manufacturing for both OLEDs and LCDs.
But OLEDs have a significant advantage because they can be made flexible, not
just on a fixed curve. In fact, the recently introduced Samsung Galaxy Round is
actually manufactured as a flexible OLED display that is then bonded to a
curved cover glass – and it’s identical to the flat screen OLED display in the Samsung Galaxy
Note 3 that we recently tested. So the identical flat and curved displays on
the Galaxy Note 3 and Galaxy Round can be directly compared and tested
side-by-side, which we did using both extensive viewing tests and lab tests.

Even more interesting is that Samsung has also made that same OLED
display into a completely free standing flexible display, so I was able to
compare three essentially identical 5.7 inch 1080p OLED displays in their flat,
curved, and flexible display formats side-by-side. This article is my analysis
of curved and flexible displays for Smartphones…

Concave Screen

First of all, the curvature on the Galaxy Round is fairly small – the
left and right edges of the screen are just 2.66 mm (0.10 inch) higher than the
center, so the effect is subtle, but it’s very important. The screen is curved
in only one dimension – its cylindrically curved along the horizontal direction
when the Smartphone is held in the standard Portrait mode. And it’s concave
rather than convex – similar to a handheld magnifying mirror, which is also
slightly concave, but it is curved in two dimensions rather than one. Keep this
concave magnifying mirror analogy in mind…

Form Factor and Screen Privacy

The Galaxy Round and Galaxy Note 3 have similar outer dimensions because
the effect of the small curvature on the overall size is small. The Round is
slightly thinner but has almost identical width and height as the Note 3. It is
more comfortable to hold because the hand nicely fits the entire curved back
instead of just holding it along the left and right edges. It also improves
screen privacy because the curvature makes it harder for other people to see
the screen (unless you intentionally turn it to show them).

Screen Readability in Ambient Light

Smartphones are almost always used in significant ambient light. All
display screens reflect that ambient light, which washes out the colors and
image contrast, and makes it harder to read the screen. To see by how much,
turn off the display but hold the Smartphone as if you’re using it and then
walk around your normal environment, both indoors and outdoors. All of the
reflections from lamps, ceiling lights, windows, direct and indirect indoor and
outdoor sunlight, and even the reflection of your face are still there when the
display is on. That requires you to increase the screen brightness to counter all
of that ambient light interference. It’s so important that peak screen
brightness is generally considered one of the most important display parameters
by most consumers. But the higher the screen brightness the more power the
display uses, and the shorter the running time on battery.

So if there is a way to reduce those screen reflections, it will not
only improve the screen readability, image contrast, color accuracy, and
overall picture quality, but also increase the running time on battery. One way
is to reduce the screen Reflectance. It has been steadily coming down, and the
Galaxy Note 3 and Galaxy Round have about
5 percent Reflectance, among lowest I have ever measured for mobile
displays.

But there is a really innovative way to further cut down on screen
reflections – and that is by introducing a small amount of screen curvature,
like on the Galaxy Round…

Reflections from a Curved Screen

The concave screen shape on the Galaxy Round cuts down on reflections
from the surrounding ambient light two ways: first, by reducing the screen’s 180 degree opening angle, which
eliminates reflections from some ambient light coming from the sides. Second, from specular
mirror reflections off the concave screen, because the curvature directs
reflected ambient light coming from behind away from the viewer’s line of
sight. This is very important because you want to minimize the amount of
ambient light that is seen reflected off the screen.

Curved Screen Magnification

But the most interesting and important result of the slightly curved
Galaxy Round screen is that it magnifies the sizes of all of the objects that
it reflects, just like a concave mirror that I mentioned above. As it turns
out, that substantially cuts down on the interference of light reflections from
ambient light in three ways:

First: when you are holding a flat
screen, at normal viewing distances it reflects not only your face (which is
typically in shadow) but all of the light coming from directly behind and
around your head, which almost always is considerably brighter than your face. Check this out right now by holding up your Smartphone with
the display turned off. But with the curved
Galaxy Round held at normal viewing distances, your face is magnified so that
it always fills the entire screen so that you don’t see the much brighter light
coming from behind you. As a result, there is typically a large reduction of
reflected ambient light, both indoors and especially outdoors. This effect is
the first major display improvement resulting from the curvature.

Second: because your face is being
magnified horizontally by a factor of 2 or more (depending on the viewing
distance), the brightness of the reflected image is also reduced (because it is
being spread out by the magnification). This is equivalent to reducing the
screen Reflectance and is the second major display improvement resulting from
the curvature. Note that the magnified facial reflection is now so dark that
you can’t use the Smartphone as a mirror for personal grooming…

Third: the curved screen on the Galaxy
Round has a focal distance of about 16 inches, which is also comparable to the
typical viewing distance. As you increase your viewing distance from a typical
minimum of 8 inches, the horizontal magnification increases rapidly, up from a
factor of 2 until it becomes effectively infinite at about 16 inches viewing
distance. Because the reflection of your face is being magnified by a large
factor, your facial features appear blurred and become increasingly featureless
and effectively invisible. That significantly reduces the visual interference
from the screen reflections. This featureless reflection is the third major
display improvement resulting from the curvature.

All these effects were clearly visible by holding and comparing the
Galaxy Round and Galaxy Note 3. The result is a very large improvement of the
display in ambient light. This not only substantially improves screen
readability, image contrast, color accuracy, and overall picture quality, but
can also increase the running time on battery because the screen brightness and
display power can be lowered due to the reduced interference from ambient light
reflections.

On the other hand, if you aren’t looking more or less directly at your
Smartphone, then the screen will be pointing in some other direction and
reflecting other things. In that case your face may only partly appear in the
screen reflection, or even not at all if it’s significantly angled. Anything
more than a few feet away from the curved screen won’t be noticeably magnified,
so the above advantages in this case will be reduced, but this also means you
are paying less attention to the screen. Once you hold it back up all of the
improvements mentioned above will return.

Flexible Displays

Finally, the icing on the cake was looking at the same OLED display on
the Galaxy Round and Galaxy Note 3 as a completely free standing flexible
display. So I was able to bend and adjust the display in any direction or way
and to any degree that I wanted while comparing it to the Galaxy Round and
Galaxy Note 3. Most of the time people just want to bend the flexible screen
into contortionist orientations, but instead I explored the effects of subtle
changes in its curvature on the reflections from all the surrounding ambient
light. The curved Galaxy Round already performs extremely well when held like a
Smartphone, so I explored how the three displays looked when lying down on a
table. The curved Galaxy Round performed better than the flat Galaxy Note 3,
but with some minor bending of the flexible display I was able to further
reduce ambient light that was washing out the screen, including an annoying
overhead table light. Flexible displays will have lots of applications, but a
very important one is improving screen visibility by subtly bending away
distracting light reflections. Curved is great but bendable is even better…

There’s more… Flexible OLED displays are manufactured using a flexible
plastic substrate, so they don’t have the glossy cover glass used on virtually
all existing mobile displays. That provides three more advantages: first, the screen
Reflectance is lower because is doesn’t have the extra layer of cover glass. Second, the plastic bendable
screen is not as glossy as the cover glass so it has a very slight matte haze
finish, which cuts down on the specular mirror reflections. Third, without the cover
glass the OLED display appears to be right on the surface of the screen, which
is quite visually striking!

Finally, a subtle but very important technical point is that the Galaxy
Round, which has the new flexible OLED display, and the Galaxy Note 3, which
has the traditional rigid glass OLED display, both had virtually identical
performance in both our lab tests and viewing tests (other than the enhanced
optical effects resulting from the curved screen discussed above).

Curved and Flexible Display Conclusions:

Introducing a slightly curved cylindrically concave screen is a very
important and major innovation in Smartphone display technology – very far from
being a marketing gimmick as has been widely reported. The Galaxy Round screen
curvature is very subtle, just 0.10 inches away from flat, which is similar to
the slight curvature in a handheld magnifying mirror. But that small curvature
is the key to a series of optical effects that result in significantly reducing
interference from reflected ambient light by a large factor. It substantially
improves screen readability, image contrast, color accuracy, and overall
picture quality, but can also increase the running time on battery because the
screen brightness and display power can be lowered due to the reduced light
interference from ambient light reflections. To see this for yourself and understand
the size and importance of this effect, turn off the display but hold your
Smartphone as if you’re using it and then walk around your normal environment,
both indoors and outdoors.

All of the performance enhancements that we have discussed were clearly
visible by holding and comparing the curved screen Galaxy Round with a
virtually identical flat screen Galaxy Note 3. The Galaxy Round is currently
only available in Korea due to the limited production capability for curved
OLED displays. Samsung has informed me that as the production volume is
increased, it will be introduced in other countries.

While LCDs can now be
manufactured with curved glass screens, OLEDs can be manufactured with entirely
flexible screens on a plastic substrate. The Galaxy Round is actually
manufactured as a flexible OLED display that is then bonded to a curved cover
glass. Maintaining it as a purely flexible display provides even greater
performance and functionality enhancements. Flexible displays will have lots of
applications, but a very important one is improving screen visibility by subtly
bending away distracting light reflections. Curved is
great but bendable is even better…

It will
take several years before flexible displays become incorporated into actual
production Smartphones and then into entirely new products, uses, and
applications. It’s clear that flexible displays will have a profound effect on
the use of most display based products starting in the very near future. The
display world isn’t flat anymore, and in a few years it won’t even have to be
round…

About the Author

Dr. Raymond Soneira is
President of DisplayMate Technologies Corporation of Amherst, New Hampshire,
which produces video calibration, evaluation, and diagnostic products for
consumers, technicians, and manufacturers. See www.displaymate.com. He is a research
scientist with a career that spans physics, computer science, and television
system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from
Princeton University, spent 5 years as a Long-Term Member of the world famous
Institute for Advanced Study in Princeton, another 5 years as a Principal
Investigator in the Computer Systems Research Laboratory at AT&T Bell
Laboratories, and has also designed, tested, and installed color television
broadcast equipment for the CBS Television Network Engineering and Development
Department. He has authored over 35 research articles in scientific journals in
physics and computer science, including Scientific American. If you have any
comments or questions about the article, you can contact him at dtso.info@displaymate.com.

About DisplayMate Technologies

DisplayMate Technologiesspecializes in proprietary
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accuracy for all types of displays including video and computer monitors,
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our intensive scientific analysis of Smartphone and Smartphone mobile displays
– before the benefits of our advanced mathematical DisplayMate Display Optimization
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